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1. Field of Invention
The invention is directed towards a transmitting/receiving device for amplification of the transmitted signals between a stationary transmitting station and a mobile transmitting station in a full-coverage radio network and also towards a process for operating such a transmitting/receiving device.
2. Description of the Related Art
The various possibilities of mobile radiotelephones were recognised very quickly by the business world and in the meantime have formed the basis for the success of many a businessman. This results from the advantage that, in principle, a person can be reached everywhere, and consequently at any time, via a mobile radiotelephone. However, this does not apply without restriction. For, as a consequence of the low transmitting power of mobile radiotelephones, house walls of normal thickness are already able to bring about such an attenuation of the radio signals that the received field strength is insufficient for communication. Therefore the communication often fails precisely at those times when a businessman is located together with his mobile radiotelephone in his own house or office. As a result, many a business deal can slip though his fingers, and many businessmen would be pleased if the received field strength in their own house or office were sufficient for communication.
Co-channel broadband repeaters have already been employed for this purpose. In this case the decoupling between transmitting aerial and receiving aerial is very critical, and interference phenomena arise as a result of the amplification of additional frequencies which are not required, as well as, in certain circumstances, a heightened background noise, so these devices have not found widespread application in practice.
Although a transmitting/receiving device for amplification of the radio signals in a closed building has become known from EP 0 342 858, the installation effort associated with such a device is considerable, since on the one hand an aerial has to be placed on the roof of the building, and on the other hand this transmitting/receiving device is provided with a band-pass filter, the frequency of which has to be tuned by a person skilled in the art to the frequencies that are used in the radio cell in question. The effort associated with the installation of such a system is therefore enormously high.
This results in the problem giving rise to the invention, namely to create a transmitting/receiving device for selective amplification of, exclusively, the channels pertaining to a radio cell, which can be installed without prior knowledge and also with minimal effort and consequently also by technically unskilled people.
The invention solves this problem by means of a device for automatic recognition of the radio channels or radio frequencies that are used in a radio cell pertaining to the radio network. Although the transmitting/receiving device according to the invention is, on the one hand, transparentxe2x80x94that is to say, it is not perceived at all, either by the radio network or by a mobile transmitting stationxe2x80x94it is nonetheless provided with its own intelligence which permits it to be harmoniously integrated into the xe2x80x9cfrequency landscapexe2x80x9d of the radio network. With a transmitting/receiving device of this type, therefore, no manual equalisation whatsoever of filter frequencies has to be carried out; rather, the setting-up procedure in accordance with simple rules which are specified in an operating manual is sufficient.
The channel spectrum of conventional mobile radio networks encompasses several types of radio channel: in each radio cell there is at least one broadcast control channel (bcch) which is constantly available for all mobile radio units and which, in the event of a call, allocates to said mobile radio units one of several slow dedicated control channels (sdcch) on which the transmission parameters for a radio link to be established between the radio network and the mobile station are then exchanged. For the actual communication, use is then made of traffic channels (tch). According to the GSM standard, each frequency channel comprises eight time-slots, each of which can be used as a bcch, sdcch or tch. On the other hand, the bcch, sdcch and tch which are used in a radio cell must not be assigned to the same frequency channel. In the following, the term xe2x80x9cchannelxe2x80x9d is to be interpreted to mean xe2x80x9cfrequency channelxe2x80x9d. Since these frequency channels may be distinctly remote from one another in the frequency spectrum, the invention provides that a parallel transmitting/receiving branch, but preferably several such branches, is/are arranged in the transmitting/receiving device according to the invention.
Depending on the channel structure, of the radio network in question, the slow dedicated control channels and/or the traffic channels may in each instance be combined to form neighbouring groups. In such a case it is possible that the bandwidth of a transmitting/receiving branch comprises not only a single radio channel but several radio channels simultaneously, so that the latter are amplified jointly.
In order that the transmission frequencies of the broadcast control channel, of a slow dedicated control channel and/or of a traffic channel can be adapted arbitrarily so as to conform to the local conditions in the radio cell in question pertaining to the radio network, the transmitting frequencies of different transmitting/receiving branches should be capable of being set independently of one another. This also applies, for example, to transmission branches which are connected in antiparallel manner for bidirectional communication.
On an increasing scale, radio networks are currently being packed by frequency-converting repeaters which, however, with the exception of the frequency conversion, are otherwise transparent. Such repeaters define separate radio cells with transmitting frequencies that are delimited with respect to the neighbouring radio cells and have the characteristic feature that a radio signal with identical content is transmitted on the uplink and downlink sides of the repeater via two different transmitting frequencies, whereby the channel-number that is transmitted on the channel in question for the purpose of identification coincides exclusively with the transmission channel of the radio interface on the downlink side between the frequency-converting repeater and a mobile transmitting station, whereas this channel information for the xe2x80x9cinternal-networkxe2x80x9d communication between the actual, stationary transmitting station and the frequency-converting repeater does not coincide with the channel frequency that is used there. Here the invention provides that the transmitting/receiving device according to the invention is operated parallel to such a frequency-converting repeaterxe2x80x94that is to say, it is directly coupled on the uplink side to the actual, stationary transmitting station and directly coupled on the downlink side to the mobile transmitting station. In this case the transmitting/receiving device according to the invention has to reproduce the frequency conversion of the repeater, for which purpose it is necessary that the frequencies of the uplink-side and downlink-side radio interfaces of a transmitting/receiving branch are capable of being set independently of one another. By this means, the transmitting/receiving device according to the invention can be operated both in radio cells without frequency conversion and in radio cells with frequency-converting repeaters.
To the extent that the transmitting/receiving device in question is operated in the radio cell of a frequency-converting repeater, the received signals and the signals transmitted further are decoupled from one another in frequency terms, so that it is possible to integrate an uplink-side aerial and a downlink-side aerial within the housing of the transmitting/receiving device. In this case it is even possible to make use of a single aerial for the uplink-side and downlink-side radio interfaces.
In order to obtain an adequate received field strength at the uplink-side radio interface, the invention recommends that the aerial in question be capable of being fastened to a window. In this regard it may be a question, for example, of a type of self-adhesive foil with enclosed aerial.
The primary criterion for the recognition of a radio channel that is used in a radio cell is constituted by the received field strength of said radio channel. With a view to ascertaining said received field strength, one or more measuring devices are present in the transmitting/receiving device. In order not to make the internal circuit of the transmitting/receiving device according to the invention too complicated, the invention provides that the devices for measuring the received field strength are each assigned to a transmitting/receiving branch. The measuring devices can consequently be totally integrated into the circuits of the transmitting/receiving branches.
Another criterion with a view to orientation in the xe2x80x9cchannel spectrumxe2x80x9d of the radio cell in question is constituted by the information that is transmitted on the individual radio channels. In order to ascertain this information, the transmitting/receiving device according to the invention is provided with one or more devices for demodulation and/or decoding of radio signals. Here too, a separate demodulation device and/or decoding device may be assigned to each transmitting/receiving branch. The demodulation device or decoding device according to the invention is preferably coupled, or capable of being coupled, to the output of a receiving branch.
Furthermore, the transmitting/receiving device according to the invention has to recognise whether it is located in a radio cell with a direct radio link between a stationary transmitting station and a mobile transmitting station or in a radio cell that is supplied via a frequency-converting repeater. For this purpose, one or more modular units are provided in the transmitting/receiving device according to the invention for comparing the radio channel assigned to a channel frequency which is actually used with the channel-number that is received and demodulated on the frequency in question. In this connection it is favourable to convert the information in question into digital numbers and to compare the latter with one another by means of a comparator of binary design. These modular comparison units may also be present separately for each transmitting/receiving branch.
Finally, the radio channels or frequencies that have been found should be saved in a memory, so that in the event of a later channel command the transmitting/receiving device according to the invention can locate the corresponding transmitting frequencies immediately.
The channel-recognition device pertaining to the transmitting/receiving device according to the invention has to be operated in accordance with an ingenious process, in order to track down, in all possible types of mobile radio network, the channels that are used in the radio cell in question. In this connection, on the one hand different frequency ranges, as well as different signal codes, have to be taken into account. Furthermore, the channel-recognition device has to establish whether it is located in a radio cell with a direct radio link between a stationary transmitting station and a mobile radio station or in a radio cell with a frequency-converting repeater. In the latter case, both frequencies have to be ascertained for each channel, so that a parallel connection, in signal terms, with respect to the repeater which has been installed by the network operator is possible. With this channel recognition there may, in turn, be various preconditions: depending on the radio network, it is possible that the two frequencies of a channel are spaced from one another by a frequency offset which is fixed in each case, or it may be a question of a radio network with arbitrary channel allocations on the uplink and downlink sides of a repeater which has been installed by the operator. As elucidated in the following, a channel-recognition device according to the invention can be operated in accordance with a process that satisfies all the above requirements.
This process is distinguished in that, in a first step, the received field strength of the channels which are allocated to a radio network is ascertained and one or more broadcast control channels (bch) are ascertained from the channels having the greatest received field strength and in that said broadcast control channels are subsequently decoded, in order to ascertain, on the basis of the information transmitted there, the channels or frequencies of one or more slow dedicated control channels (sdcch) and/or traffic channels (tch). Of course, these steps may be preceded by an initialisation phase in which the owner of a transmitting/receiving device according to the invention sets the radio network that is utilised by his mobile radiotelephone with the aid of a selector switch. On the basis of the position of this selector switch the channel-recognition device can immediately find out from an internal memory the frequency range that is used by this radio network and possibly further characteristic features of this radio network, for instance whether or not use is made of frequency-converting repeaters. In a first step a favourable broadcast control channel is sought that is received with sufficient field strength by the transmitting/receiving device according to the invention. For this purpose, firstly a part of the frequency range or the entire frequency range of the radio network in question is gauged with regard to the received field strength which is related in each instance to a channel, and a note is made of the channels with the highest received field strengths. These channels are then decoded, in order to establish which channels serve for broadcast control. If the channel-recognition device has found an optimal broadcast control channel by this means, it can further evaluate the information that is transmitted on said channel.
In this connection it is possible that messages are transmitted on the broadcast control channels at predetermined time-intervals which contain information about the channels or frequencies which are used in the radio cell in question and that these messages are evaluated by the channel-recognition device. This measure according to the invention presupposes the co-operation of the network operator in question, who assists the installation of individual signal-amplification systems by generating appropriate messages and consequently makes his radio network more attractive for prospective customers. To the extent that a network operator makes such radio messages available in his radio network, the initialisation phase of a channel-recognition device according to the invention turns out to be relatively simple: after selection of an optimal broadcast control channel the latter is decoded, and a wait is observed for the next information message. The latter is then evaluated, in order to obtain all the necessary information for operation of the transmitting/receiving device according to the invention. It is advisable to examine regularly the received field strength of the selected broadcast control channel, as well as the content of the information messages transmitted there, since changes in the channel allocations are sometimes made by a network operator.
In addition to the information about the channels or frequencies that are used in the radio cell in question, by this means information can also be transmitted from which the channel-recognition device according to the invention can deduce whether it is located in a radio cell with frequency-converting repeaters which have been installed by the operator or in a radio cell that is supplied directly. from a stationary transmitting station; furthermore, information can be transmitted which contains an explanation about frequency offsets that are used in the radio cell in question, in particular whether in the case of frequency-converting repeaters a fixed frequency offset is observed. Furthermore, it is possible to transmit recommendations as to which radio zones or radio channels a transmitting/receiving device according to the invention is to assign itself to, to the extent that a selection option exists with regard to the received field strength. On the other hand, the traffic on particular channels or in particular radio cells or in radio subzones defined by other, frequency-converting transmitting stations can also be, measured, and in the event of utilisation at full capacity or overload an appropriate message can be generated which prevents additional transmitting/receiving devices according to the invention from being assigned to radio cells that are already overloaded.
If no such radio messages are made available in a mobile radio network, the channel-recognition device itself has to seek the channels in question (slow dedicated control channels sdcch and traffic channels tch). For this purpose, channel commands transmitted on the broadcast control channel that has been set are evaluated in a further step by the channel-recognition device. By this means, slow dedicated control channels sdcch can firstly be found, and subsequently, as a result of the decoding thereof, the traffic channels tch that are used in the radio cell in question. By this means it is possible for the device according to the invention to ascertain gradually all the relevant channels in the radio cell in question.
According to the process described above, it is possible to ascertain all the channels pertaining to the radio interface between a stationary transmitting station or a frequency-converting repeater and a mobile station. However, in a radio cell with a frequency-converting repeater it is desirable that the transmitting/receiving device according to the invention also ascertains the channels and frequencies pertaining to the radio interface between the stationary transmitting station and the frequency-converting repeater. To this end, firstlyxe2x80x94beginning with the selected broadcast control channelxe2x80x94the channel-number that is transmitted and decoded there is compared with the channel frequency actually received. In the event of coincidence, the channel-recognition device knows that in this case it is a question of a radio interface to a mobile station; in the event of a discrepancy between these two channel-numbers, the transmitting/receiving device according to the invention receives a channel pertaining to the radio interface between the stationary transmitting station and a frequency-converting repeater.
In a radio cell with frequency conversion the transmitting/receiving device according to the invention is switched parallel to the repeater which has been installed there by the network operator, in that the transmitting/receiving device on the uplink side is tuned to the actual frequency of a channel, the actual channel frequency of which does not coincide with the transmitted channel-number, and on the other hand in that the transmitting/receiving device on the downlink side is tuned to the transmitted channel-number. On the one hand, this operation offers the advantage that the signal delay is reduced to a minimum. On the other hand, the signals of the transmitting/receiving device according to the invention on the uplink and downlink sides are separated from one another in frequency terms and are consequently optimally decoupled from one another, so that interference phenomena are almost totally ruled out.
The channels or frequencies of the slow dedicated control channels sdcch and traffic channels tch are also set, according to the above rule, so as to be separated from one another on the uplink and downlink sides. For this purpose, the relevant frequencies of these channels at the radio interface between the stationary transmitting station and the frequency-converting repeater also have to be determined. According to the invention this can be done by the actual channel frequency of a slow dedicated control channel sdcch and/or traffic channel tch, to the extent that the latter does not coincide with the transmitted channel-number, being ascertained by comparison of the transmitted messages with the messages transmitted on further channels that have been selected with regard to their received field strength. This process is necessary if neither an information message is made available by the network operator nor a fixed frequency offset is observed between channels that are assigned to one another pertaining to the two radio interfaces of a frequency-converting repeater. In such a case, further channels with sufficient received field strength are decoded, and the information and/or messages received there are compared with the corresponding information contents of the radio interface between the frequency-converting repeater and the mobile station, in order to establish a correlation. This process is repeated until such time as the second frequency, which is used on the uplink side of the frequency-converting repeater, of the information channel in question has been found.
In order to perform such a comparison, several receiving branches of the transmitting/receiving device according to the invention may be operated simultaneously. If this is not possible, messages transmitted sequentially during a connection set-up can be drawn upon for the information comparison.
In order to obtain the acquired information for further operation of the transmitting/receiving device according to is the invention, the invention finally provides that the channel-numbers and the actual channel frequencies corresponding to one another are stored in correlated form. Accordingly, if the device according to the invention decodes a channel command at a later time, by read-out of the memory it is in a position to recognise the frequencies immediately to which the transmitting/receiving devices on the uplink and downlink sides are to be set.